1. Field
Example embodiments relate to an oxide semiconductor and a thin film transistor (TFT) including the same, and more particularly, to an oxide semiconductor obtained by adding a new material to gallium-indium-zinc oxide (GIZO) and a TFT including the same.
2. Description of the Related Art
Thin film transistors (TFTs) may be used in various application fields and, particularly, may be used as switching and driving devices of display apparatuses and as selection switches of cross-point type memory devices.
While liquid crystal display (LCD) apparatuses may be mainly used as display panels in televisions (TVs), a vast amount of research on organic light-emitting display (OLED) apparatuses that may also be applied to TVs is being conducted. TV display technologies may be developed according to demands of the market. Market demands may include demand for: large-scaled TVs or digital information display (DID) apparatuses, low price, and high definition (high resolution, excellent color rendition, brightness, contrast characteristics, and high color reproducibility), etc. In order to satisfy these demands, substrates such as glass substrates may be required to become larger and TFTs to be used as switching and driving devices of display apparatuses may be required to have high performance.
An example of a TFT used as a switching or driving device of a display apparatus may be an amorphous silicon (a-Si) TFT which may be uniformly formed on a large substrate over 2 meters (m) in length at a low cost, and may the most widely used TFT. However, TFTs may be required to have high performance as display apparatuses require high-definition characteristics and large sizes, and thus the display apparatuses may be regarded as being limited by the operating capabilities of typical a-Si TFTs having a mobility of about 0.5 cm2/Vs. Thus, a high-performance TFT having a higher mobility than an a-Si TFT, and a technology of manufacturing the high-performance TFT may be required.
A polysilicon (poly-Si) TFT, having a much higher performance than an a-Si TFT may have a mobility of several tens to several hundred cm2/Vs. Thus a poly-Si TFT may have a sufficiently high performance to be applied to high-definition display apparatuses that are not easily implemented by using a-Si TFTs. Also, poly-Si TFTs have less device characteristic deterioration than a-Si TFTs. However, the process of manufacturing poly-Si TFTs may be more complicated than that of a-Si TFTs, and thus additional costs may increase. Thus, although a poly-Si TFT may be appropriately applied to a high-definition display apparatus or an OLED apparatus, application of poly-Si TFTs may be limited due to higher costs than a-Si TFTs. Also, poly-Si TFTs have not been implemented on large substrates over 1 m in length until now due to, for example, manufacturing equipment limitations or uniformity defects. As a result, poly-Si TFTs may not be easily applied to TV products.
Accordingly, a new TFT having advantages of both a-Si TFTs and poly-Si TFTs may be required, and research is being actively conducted into such a new TFT. A representative example of such a device may be an oxide semiconductor device.
Among oxide semiconductor devices, zinc oxide (ZnO)-based TFTs are currently attracting attention. Until now, ZnO-based materials such as ZnO, indium-zinc oxide (IZO), and ZnO or IZO in which, for example, gallium (Ga), magnesium (Mg), aluminum (Al), or iron (Fe) may be doped have been introduced. A ZnO-based semiconductor device may be manufactured through a low-temperature process and has an. amorphous phase, and thus may be easily implemented on a large substrate. Also, a ZnO-based TFT has high mobility and an excellent electric characteristic like the poly-Si TFT. Currently, research is being conducted in order to use an oxide semiconductor material layer having a high mobility, in particular, a ZnO-based material layer in a channel area of a TFT.